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Old algo for ID derivation was not in fact memory-hard since Salsa20 is seekable, so take two.

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This commit is contained in:
Adam Ierymenko 2013-10-07 12:48:27 -04:00
parent 0c8614b9c6
commit 343b7f44fc
2 changed files with 42 additions and 16 deletions
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54
node/Identity.cpp
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@ -38,26 +38,51 @@
// These can't be changed without a new identity type. They define the
// parameters of the hashcash hashing/searching algorithm.
// Hashcash halting criteria
#define ZT_IDENTITY_GEN_HASHCASH_FIRST_BYTE_LESS_THAN 5
// Amount of memory for memory-hardness
#define ZT_IDENTITY_GEN_MEMORY 8388608
// Step distance for mixing genmem[]
#define ZT_IDENTITY_GEN_MEMORY_MIX_STEP 128
namespace ZeroTier {
// A memory-hard composition of SHA-512 and Salsa20 for hashcash hashing
static inline void _computeMemoryHardHash(const void *publicKey,unsigned int publicKeyBytes,void *sha512digest,unsigned char *genmem)
static inline void _computeMemoryHardHash(const void *publicKey,unsigned int publicKeyBytes,void *digest,void *genmem)
{
// Step 1: hash key to generate Salsa20 key and nonce
SHA512::hash(sha512digest,publicKey,publicKeyBytes);
// Hash publicKey[] to obtain Salsa20 key
SHA512::hash(digest,publicKey,publicKeyBytes);
// Step 2: copy key into genmen[], zero rest, encrypt with Salsa20
Salsa20 s20(sha512digest,256,((char *)sha512digest) + 32);
memcpy(genmem,publicKey,publicKeyBytes);
memset(genmem + publicKeyBytes,0,ZT_IDENTITY_GEN_MEMORY - publicKeyBytes);
// Generate genmem[] bytes of Salsa20 key stream
memset(genmem,0,ZT_IDENTITY_GEN_MEMORY);
Salsa20 s20(digest,256,(char *)digest + 32);
s20.encrypt(genmem,genmem,ZT_IDENTITY_GEN_MEMORY);
// Step 3: hash the encrypted public key and the rest of the
// genmem[] bytes of Salsa20 key stream to yield the final hash.
SHA512::hash(sha512digest,genmem,ZT_IDENTITY_GEN_MEMORY);
// Do something to genmem[] that iteratively makes every value
// possibly dependent on every other value with a nontrivial
// probability.
for(unsigned int i=0;i<ZT_IDENTITY_GEN_MEMORY;i+=ZT_IDENTITY_GEN_MEMORY_MIX_STEP) {
s20.encrypt((char *)genmem + i,(char *)genmem + i,8);
uint64_t x = *((uint64_t *)((char *)genmem + i));
if ((x / 7ULL) < 0x1249249249249249ULL) {
s20.encrypt(&x,&x,8); // also causes PRNG state to depend on genmem[]'s state
for(unsigned int k=0;k<8;++k,x>>=8)
++((unsigned char *)genmem)[(uintptr_t)x % ZT_IDENTITY_GEN_MEMORY];
} else {
for(unsigned int k=0;k<8;++k,x>>=8)
--((unsigned char *)genmem)[(uintptr_t)x % ZT_IDENTITY_GEN_MEMORY];
}
}
// Mix in publicKey[] again, ensuring all entropy is used
for(unsigned int i=0;i<publicKeyBytes;++i)
((unsigned char *)genmem)[i] ^= ((const unsigned char *)publicKey)[i];
// Compute final digest from final genmem[]
SHA512::hash(digest,genmem,ZT_IDENTITY_GEN_MEMORY);
}
// Hashcash generation halting condition -- halt when first byte is less than
@ -65,20 +90,21 @@ static inline void _computeMemoryHardHash(const void *publicKey,unsigned int pub
struct _Identity_generate_cond
{
_Identity_generate_cond() throw() {}
_Identity_generate_cond(unsigned char *sb,unsigned char *gm) throw() : sha512digest(sb),genmem(gm) {}
_Identity_generate_cond(unsigned char *sb,char *gm) throw() : sha512digest(sb),genmem(gm) {}
inline bool operator()(const C25519::Pair &kp) const
throw()
{
_computeMemoryHardHash(kp.pub.data,kp.pub.size(),sha512digest,genmem);
return (sha512digest[0] < ZT_IDENTITY_GEN_HASHCASH_FIRST_BYTE_LESS_THAN);
}
unsigned char *sha512digest,*genmem;
unsigned char *sha512digest;
char *genmem;
};
void Identity::generate()
{
unsigned char sha512digest[64];
unsigned char *genmem = new unsigned char[ZT_IDENTITY_GEN_MEMORY];
char *genmem = new char[ZT_IDENTITY_GEN_MEMORY];
C25519::Pair kp;
do {
@ -100,7 +126,7 @@ bool Identity::locallyValidate() const
return false;
unsigned char sha512digest[64];
unsigned char *genmem = new unsigned char[ZT_IDENTITY_GEN_MEMORY];
char *genmem = new char[ZT_IDENTITY_GEN_MEMORY];
_computeMemoryHardHash(_publicKey.data,_publicKey.size(),sha512digest,genmem);
delete [] genmem;